A capacitive welder is advantageous in that the capacitive welder does not need a large facility for receiving electric power, if compared to a general AC welder, because the capacitive welder stores welding electric power in a welding capacitor in a longer time than a discharge time and discharges the electricity at once. The capacitive welder is also advantageous in that welding marks (burning) are hardly created at welded portions and distortions are small because the object to be welded is only superheated to a small extent. Because of such advantages, the capacitive welder is employed for any size of industrial facility (from small to large industrial facilities).
In general, the capacitive welder uses a capacitor bank as a welding capacitor, which includes a plurality of parallel-connected capacitors. Because the resistance welding method using the capacitive welder is well known, the resistance welding method is not described here in detail. In brief, the welding capacitor is charged by a charging circuit, and the charging circuit is turned off when the charging voltage of the welding capacitor increases to a predetermined value (e.g., about 450V). Then, a discharge switch is turned on to allow a steeply increasing pulse current to flow to a primary winding of a welding transformer. A pulse welding current, which is significantly greater than the primary winding current, flows to a secondary winding of the welding transformer. This welding current flows in the object to be welded, through welding electrodes and therefore the object is welded.